310 research outputs found
Thermal X-ray composites as an effect of projection
A new possibility to explain the nature of thermal X-ray composites (TXCs),
i.e. a class of supernova remnants (SNRs) with a thermal X-ray centrally-filled
morphology within a radio shell, as a projection effect of the 2- or
3-dimensional shell-like SNR evolved in a nonuniform medium with scale-height
<10 pc is proposed. Both X-ray and radio morphologies, as well as the basic
theoretical features of this kind of SNR and the surrounding medium, are
considered. Theoretical properties of a shell-like SNR evolved at the edge of a
molecular cloud correspond to the observed properties of TXCs if the gradient
of the ambient density does not lie in the projection plane and the magnetic
field is nearly aligned with the line of sight. So, at least a part of objects
from the class may be interpreted within the framework of the considered
effect. The proposed model suggests that SNRs with barrel-like radio and
centrally-brightened thermal X-ray morphologies should exist. The model allows
us to consider TXCs as prospective sources of proton origin gamma-rays.Comment: 7 pages, 4 figures; added one figure, few subsections and references,
corrected typos; accepted for publication in A&
Analytic Solutions for the Evolution of Radiative Supernova Remnants
We present the general analytic solution for the evolution of radiative
supernova remnants in a uniform interstellar medium, under thin-shell
approximation. This approximation is shown to be very accurate approach to this
task. For a given set of parameters, our solution closely matches the results
of numerical models, showing a transient in which the deceleration parameter
reaches a maximum value of 0.33, followed by a slow convergence to the
asymptotic value 2/7. Oort (1951) and McKee and Ostriker (1977) analytic
solutions are discussed, as special cases of the general solution we have
found.Comment: 5 pages, 1 figure, Astronomy and Astrophysics, accepte
Supernova remnants as cosmic ray accelerators. SNR IC 443
We examine the hypothesis that some supernova remnants (SNRs) may be
responsible for some unidentified gamma-ray sources detected by EGRET
instrument aboard the Compton Gamma Ray Observatory. If this is the case,
gamma-rays are produced via pion production and decay from direct inelastic
collisions of accelerated by SNR shock wave ultrarelativistic protons with
target protons of the interstellar medium. We develop a 3-D hydrodynamical
model of SNR IC 443 as a possible cosmic gamma-ray source 2EG J0618+2234. The
derived parameters of IC 443: the explosion energy E_o=2.7*10^{50} erg, the
initial hydrogen number density n(0)=0.21 cm^{-3}, the mean radius R=9.6 pc and
the age t=4500 yr result in too low gamma-ray flux, mainly because of the low
explosion energy. Therefore, we investigate in detail the hydrodynamics of IC
443 interaction with a nearby massive molecular cloud and show that the reverse
shock wave considerably increases the cosmic ray density in the interaction
region. Meantime, the Rayleigh-Taylor instability of contact discontinuity
between the SNR and the cloud provides an effective mixing of the containing
cosmic ray plasma and the cloud material. We show that the resulting gamma-ray
flux is consistent with the observational data.Comment: Printed in Condenced Matter Physic
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